Many modern electronic devices include wireless communications circuitry. For example, an electronic device may include wireless local area network (WLAN) communications circuitry, cellular communications circuitry, or the like. While wireless communications circuitry allows electronic devices to communicate with one another, such functionality generally comes at the cost of additional energy consumption and thus reduced battery life. Often, wireless communications circuitry is the largest consumer of energy in an electronics device. As wireless communications protocols evolve to provide higher speeds, energy consumption of communications circuitry often increases to meet the higher demands of such protocols.
Consumer demand for longer battery life from electronic devices has resulted in the development of many power-saving techniques for wireless communications. One way to conserve power consumed via wireless communications is through the use of envelope tracking. Envelope tracking involves modulating a supply voltage provided to an amplifier based on the instantaneous magnitude (i.e., the envelope) of an RF input signal provided to the amplifier. FIG. 1 illustrates the basic concept of envelope tracking. Specifically, FIG. 1 shows an amplitude-modulated RF signal 10. Conventionally, a constant supply voltage at a level sufficient to ensure adequate headroom across the entire amplitude range of the RF signal 10 would be supplied to the amplifier, as shown by line 12. This results in a significant amount of wasted energy, and thus poor efficiency, when the amplitude of the RF signal 10 is below the maximum level, as illustrated by line 14. Accordingly, an envelope power supply signal tracks the amplitude of the RF signal 10, as illustrated by line 16, and therefore increases efficiency by preventing the unnecessary expenditure of power when the amplitude of the RF signal 10 is below the maximum level.
To employ envelope tracking as described in FIG. 1, electronic devices conventionally include envelope tracking circuitry configured to generate the envelope power supply signal illustrated by line 16. Due to the fact that the gain of an RF amplifier is dependent on both the input power of an RF input signal and a supply voltage provided thereto, such circuitry may be calibrated by populating a look-up table (LUT) that stores multiple envelope tracking related voltages corresponding to various voltages of the RF signal 10 that are used to avoid distortion in the output of the amplifier. In this manner, the envelope tracking circuitry can provide the envelope power supply signal based on values stored in the LUT such that the gain of the RF amplifier remains substantially constant regardless of the input power provided to the RF amplifier. The calibration of the envelope tracking circuitry plays an important role in implementing envelope tracking for an RF amplifier. However, as the demand for increasingly smaller electronic devices, such as wearable devices, continues to rise, the area and power consumption available for such envelope tracking circuitry continues to fall. These design constraints may interfere with the ability of the envelope tracking circuitry to be properly calibrated.
In light of the above, there is a need for envelope tracking circuitry with reduced circuit area and power consumption that is capable of calibration to avoid distortion.